1. Technical Field
This disclosure relates generally to pumps and more particularly, though not exclusively to centrifugal slurry pumps which are suitable for pumping slurries.
2. Background Art
Centrifugal slurry pumps generally include a pump casing comprising a main casing part and one or more side parts. The pump may also comprise an outer housing which encases the pump casing. In this particular arrangement the pump casing provides a pump liner which is typically formed from hard metals or elastomers. An impeller is mounted for rotation within the casing about a rotation axis. The main casing part has an outer peripheral wall section with an internal surface which may be of volute form, a discharge outlet and an inlet which is at one side of the casing and coaxial with the impeller rotation axis.
The impeller typically includes one or more shrouds which may have pump out or expeller vanes which are normally on an outer face of the or each shroud. The impeller typically includes a front shroud, the outer face of which runs close to the side part of the casing with a gap therebetween. The aforementioned vanes are designed to create a pressure field that assists in countering the high pressure in the pump volute and thereby reduce the flow in the distance or gap between the front face of the shroud and the casing side part. The vanes assist in this regard, but can also initiate or accelerate wear on the impeller or casing part due to local flow eddies or vortex type flows that form due to the moving vanes.
Adjusting an impeller while a slurry pump is running is not practical due to the forces and complexity of the adjustment mechanism required. Adjusting the position of the casing side part is however practical and less complex and the adjustment can be performed at any time with the pump in operation or stopped. The flow inside a centrifugal slurry pump is complex due to the difference in slurry particle trajectories to the water flow due to their mass and momentum. Finer particles will follow the water flow, while larger particles tend to take their own path. Further complications occur due to recirculation and vortex type flows within the pump, which can become stronger at lower flows.
The pressure distribution in the volute is not always uniform because the flow in the volute does not always exactly match the flow which exits from the pump discharge. Some flow may be circulating in the volute and the volute cutwater region, which normally causes flow disturbances that result in a non-uniform pressure distribution around the volute. Eddies and vortex type flow can also form due to the cutwater disturbance to the flow pattern, and this type of flow will accelerate wear, which can also be evident in the wear on the periphery of the casing side part which is closest to the cutwater region.